Concept Art

A Rebel grunt holding an automatic rifle, which they never use in the game.
Slightly resembles the .30 cal Browning Automatic Rifle.

A female character. I guess she was suppose to be the character for those who chose to play as the first player.

Another female character, this time the one that appears as the second player. She has a hair style that strikingly resembles that of Fio's, and she even wears glasses to go with it.

Our old friend Satiko Suzuki, who appears in the first game's ending. Strangely, she seems to be walking a dog instead of praying in this picture.

Early concept of Sophia Greenville. Note how she goes from cute to serious from left to right.

Sophia in some sort of demonic dress. Touche.

Unknown character #1. Slightly resembles Eri, but with shorter hair. Eri has long hair. This one doesn't.

Unknown character #2. I couldn't determine the gender because A) there are glow marks on the cheeks, but B) no visible shading of boobs on the chest.

Unknown character #3. I've given her the nickname of "Mechanic", because she appears quite a few times near Tank Slugs.

Evil Marco in form of a dragon. Hehe.

One of the game's creators, Andy, is drawn here by Max D. An incredibly geeky aura surrounds him.

I assume that Max D. had too much time on his hands.

An early concept of the Metal Slug 2's mutants in mission 5?

The guy resembles Amadeus from Metal Slug 4, but this picture was drawn during the development stage of Metal Slug 1, with six years of gap in the time period between them.

Robotic soldiers. How gentleman of him to have his pinky up like that!

Destroyed Super Bio-boosted Soldier from the pictures above. Quite a gruesome scene that we have here.

This must be the artificial heart that the SBS units use.

I sometimes wonder what the concept artists were thinking when they draw pictures like these.
"Hey, can you spare me a grenade?"
"Sure thing!"
*plucks a grenade out of hair

Another unknown character who remotely resembles Eri.

I can't decided whether or not if this character is connected to the one in the picture above. But what I could determine was that she is evil. Evil enough to be have evil eyes, wear evil earrings and uniform, and stand in front of an evil-iciously lit background.
Ragey's note: I've been emailed about three times saying this character bears a resemblance to Captain Harlock, emphasised in these images. I never quite saw the similarity, but if people keep telling me, may as well say.

We will never know who she is, but she has a marking scribbled on her forhead.
It reads, "metasura", which is a slang term in Japanese for "Metal Slug".

Boob rockets with bandages covering the nipples. How cliche.
No idea on who the woman in the picture is, though.

"Special Madams", they call her.
She looks as if she's about to shove that rocket launcher up someone's ass.
But in the game, however, all she really does is to act like... civilian, a non-combatant.

Sergeant Allen O'Neil drowning in water.
We don't actually see him drown until Metal Slug 2. And this art is suppose to be part of Metal Slug 1's concepts.

Mrs. O'Neil.
Now you realize where Allen Jr. had come from, eh? Talk about Beauty and the Beast.

From left to right;
Chris, Hyakutaro, and Rumi.
I couldn't read out Chris's last name because of the poor resolution that the manual was scanned in, and the fact that I was too lazy to find the box that contains the damned thing.
I don't know about Chris, but the really freaky thing about those characters is that they were listed up in the Playstation editions of Metal Slug 1, on page 27. But you never see them in the actual game.

This must have been a really early design of the Slug Tank. The crew is unprotected, no hydraulics that allows the tanks to jump are visible, and there are no armor platings that shield the threads.

Arts for mission 1 of Metal Slug 1. If you look at the Slug Tank in the pictures, you will notice that its pair of Vulcans are missing, as well as strange barrel sticking out of the rear and missing piece of hardware on top of the turret.
The threads also look weirder. Also, the two things that stick out from the side of the thread shield are missing, too.

Early, early, early, and applied concepts of the Slug Tank. The early versions look much more cartoonish since most of the parts are round and seperated. The applied concept is more rigid and tighter looking.

The above pictures are in relation to the never-used SV-002. It's more sleek, and has a machine gun and a missile launcher instead of a vulcan. Its cannon's caliber is smaller, and the chassis profile is much lower. The headlights have also moved further to the rear of the top of the turret. The mineplow is also higher off the ground, and the all-bearing antenna has been changed from being cylindrical shape to a shape that of a cutter.

The Middle-Son class submarines. The older variant, Middle-Son 1986, has been used in the final mission of Metal Slug 1 after you fall down the bridge when Morden blows it up.
The newer one, Middle-Son 1999, is used in the first mission of Metal Slug 1 as a derelict submarine.

To the left is the old design of Type-2 Di Cokka. In the middle is a very funky design of it that got scrapped. To the right is the one that has been used for the final game.
The picture to the right shows how close the tank looked like M3 Lee battle tank used by the Americans during World War II.

Early, early, and applied concepts of the Type-2B Melty Honey.
The first picture shows the Melty Honey as a battle tank. The ones in the second and third makes it resemble a fire-support vehicle, with its open top crew compartment. The difference between the second and third designs is that the third has the spikes on its front armor, while the previous one does not.

To the left is the old design of the Type-3 Bull Chan. To the right is the one that has been used for the final game.
But more importantly, the first picture shows how the designers were planning to add more sophisticated projectile/armor characteristics into the game, seeing how the shell is being bounced off of the top armor of that vehicle.

Early, early, and applied concepts of the Type-4 Girida-O battle tank.
The picture in the middle makes the tank resemble the M4A3 Sherman used by the Allies during World War II.

Early and applied concepts of the Type-5 Iron Iso assault tank.
The first picture makes the tank resemble the German SdKfz173 Jadgpanther, although the latter resembles the PzKw VI Tiger.

Anti-aircraft gun. There was suppose to be another AFV for the Rebellion designated as "Type-6" which serves as an anti-aircraft vehicle. But it seems that it was scrapped due to the fact that there were no controllable aircraft for the players in Metal Slug 1.

Another mobile ack-ack gun that never made it into the game.

Early, early, early, applied, and applied concepts of the Tani-Oh, the level 3 boss from Metal Slug 1.
The first picture shows a blocky tank with three turrets and a lot of and barrels. The second image shows a huge tank with just a huge turret with a huge gun. The third shows a huge turret mounted on its chassis that has even more smaller turrets with cannons mounted on it. It also has guns located on the side of its chassis. The final two, however, shows a completely different picture with the majority of its smaller cannons replaced by just two monstrous guns with two minelayer/Vulcan pods on each end.

Early and applied concepts of the Shoe & Karn, the level 4 boss of Metal Slug 1.
Note the difference in armaments between the old and new designs. The old one carried an anti-aircraft cannon on the back instead of a cruise missile. The new design also has a longer barrel for the gun, as well as twin auxiliary guns below it. Mineplow has been added to the new design, and the new turret now resembles that of the Girida-O's.

Both are named Land Seek, although the early concept, which is suppose to resemble American World War II GPV, is replaced by a simple transport truck that resembles German Opel truck of World War II.

A destroyed World War II German PzKw IV Ausf. H Panzer tank, which is definitely not in the game.

Well, would you look at that. Mazinger Z with an ugly face attached to it.
Not used in the game, but it says "final weapon" at the top right of the picture. I would love to cream that thing and mop the floor with it using a heavy machine gun.

Early, applied, applied, and applied concepts of the R-Shobu. The first and second pictures make the damned thing look like a child's toy, while the fourth makes it look like a joke, and the third and fifth making it much more respectable than others.
Notice how the aircraft looks considerably different by comparing the fourth picture to the others.

Early, applied, applied, and applied concepts of the Flying Tara. Strangely, the second/third and fourth concepts do not go along with each other, even though they are suppose to be the final concept of the unit in the game. The second/third picture shows a fighter-bomber, while the fourth shows a dive-bomber.

Early and applied concepts of the Hairbuster Riberts, level 2 boss from Metal Slug 1 and level 5 mini-boss from Metal Slug 3.
Not much has changed in design, except that the two engines located on its wings were replaced with a single engine that is placed on top of the aircraft.

I have... ...No clue... ...What these......Are suppose to be.
Gundam spin-offs, maybe?
But I do know that there was a seperate project for developing a spin-off of Metal Slug 1 that was going to include these robots. However, the project was cancelled due to lack of interest from the staffs due to the fact that Metal Slug 1 was suppose to be World War II oriented, not sci-fi.

The arts are for the first mission of Metal Slug 1. However, you don't actually see the flak cannons mounted on the stoneheads in the game.

Middle-Son 1999 missile submarine. The hull looks slightly different from the one used in the first mission of Metal Slug 1.

Art for mission 1 of Metal Slug 1. That's the wing of the crashed-landed Tetsuyuki gunship that you fight as the boss. Notice how many things are different, including the wingspan and the wooden platforms that you use in the game to climb up to the wing.

Art for mission 3 of Metal Slug 1. That tank is not suppose to be there, let alone exist, in the game.

Art for mission 3 of Metal Slug 1. Note that the gun turret in the picture is not in the game, but just a pile of sandbags blocking the entrance.

Art for mission 4 of Metal Slug 1. Sure, they had that shack in the game, but no machine gun was mounted in one, either.

The ship resembles an aircraft carrier, and it probably is. But the deck is angled wrong.

Arts from Metal Slug 1, although you never fight any blimps until the first mission of Metal Slug 4.
Perhaps this was all part of MEGA's plan, after all.